JP6269241B2 - Forward osmosis processing system - Google Patents

Description

  The present invention relates to a forward osmosis treatment system using a forward osmosis membrane.

  A forward osmosis treatment system is known for recovering fresh water from a treatment target liquid (feed solution) such as seawater, river water, or drainage using a forward osmosis phenomenon (see, for example, Patent Document 1). The normal osmosis phenomenon is a phenomenon in which water in a low-concentration solution permeates and moves through a membrane toward a higher-concentration (high osmotic pressure) solution.

  In the forward osmosis treatment, a draw solution (Draw Solution: hereinafter sometimes abbreviated as “DS”) having an osmotic pressure higher than that of a feed solution (hereinafter sometimes abbreviated as “FS”) is used. When DS and FS are brought into contact with each other through the osmosis membrane in the forward osmosis membrane module, water moves from FS having a low osmotic pressure to DS having a high osmotic pressure. And fresh water can be collect | recovered using various methods from DS (namely, DS which collect | recovered water from FS) after passing a forward osmosis membrane module.

  Here, FS of seawater, river water, drainage, etc. generally contains scale components (calcium carbonate, magnesium carbonate, etc.). If the concentration of the scale components exceeds the scale generation limit concentration, In some cases, the scale component is precipitated and a scale is generated.

  In the forward osmosis treatment system, water is normally separated and collected by another device from the DS after passing through the forward osmosis membrane module (that is, the DS from which water is recovered from the FS), and the remaining high-concentration DS is forward osmosis. Returned to the membrane module for reuse. In this case, if the recovery efficiency of water from the DS is increased, the DS re-supplied to the forward osmosis membrane module will inevitably become a high concentration. Although it is possible to appropriately dilute the DS by supplying the water from the water storage tank to the membrane module together with the DS as in Patent Document 1, since the recovered water is consumed once, It is undesirable in terms of recovery efficiency.

  However, when DS becomes high concentration and the osmotic pressure difference between DS and FS becomes excessively large, FS is rapidly concentrated near the surface of the forward osmosis membrane, and at the same time, scale components are also concentrated and become high concentration. Then, the scale is deposited and the scale is easily generated on the surface of the forward osmosis membrane. The scale generated on the surface of the forward osmosis membrane causes clogging of the membrane, and significantly reduces the performance of the forward osmosis membrane.

  In order to eliminate such clogging of the forward osmosis membrane, in Patent Document 1 (Japanese Patent Application Laid-Open No. 2012-250200), the concentration difference of water supplied to both sides of the forward osmosis membrane is used as a driving force for the forward osmosis membrane. A method of physically peeling and washing a substance that causes clogging of pores of the membrane attached to the surface or inside of the forward osmosis membrane by performing backwashing is disclosed.

JP2012-250200A

  However, in the method disclosed in Patent Document 1, it is necessary to periodically operate the pumps and valves in the system, interrupt the forward osmosis treatment, and perform backwashing. Further, when the scale is difficult to clean, it is difficult to restore the membrane performance even if the forward osmosis membrane is washed.

  Therefore, it is desired to provide a forward osmosis treatment system that can maintain membrane performance without cleaning the forward osmosis membrane by suppressing the generation of scale itself on the surface of the forward osmosis membrane. However, in a forward osmosis treatment system using a forward osmosis membrane, a method for suppressing scale formation on the surface of the forward osmosis membrane has not been sufficiently studied so far.

  In view of the above problems, an object of the present invention is to provide a forward osmosis treatment system capable of suppressing scale generation on the surface of a forward osmosis membrane and maintaining the performance of the forward osmosis membrane.

(1) A forward osmosis treatment system capable of moving water contained in a feed solution through a forward osmosis membrane into a draw solution having a higher osmotic pressure than the feed solution,
The forward osmosis membrane, a first chamber to which the feed solution is supplied, and a second chamber to which the draw solution is supplied, wherein the first chamber and the second chamber are the forward osmosis membrane. A forward osmosis membrane module,
A water separator for separating water from the draw solution discharged from the second chamber;
A discharge pipe for discharging the draw solution from the second chamber to the water separator;
A supply pipe for supplying the draw solution concentrated by separating water in the water separator to the second chamber;
A forward osmosis treatment comprising: a bypass pipe and a bypass pump for allowing a part of the draw solution in the second chamber to flow into the supply pipe and recirculate without passing through the water separation device. system.

(2) the feed solution includes a scale component;
The concentration of the feed solution in the first chamber when the feed solution is concentrated when water moves from the feed solution in the first chamber to the draw solution in the second chamber is the first solution. The forward osmosis treatment system according to (1), further comprising a control device for controlling the flow rate of the bypass pump so that the scale is lower than a scale generation limit concentration generated by precipitation of the scale component in one room. .

  (3) The control device includes a measuring device for measuring the osmotic pressure of the draw solution flowing in the supply pipe immediately before flowing into the second chamber, and the value of the osmotic pressure measured by the measuring device. The forward osmosis treatment system according to (2), which is a device that controls the flow rate of the bypass pump based on the above.

  ADVANTAGE OF THE INVENTION According to this invention, the normal osmosis processing system which can suppress the scale production | generation in the surface of a forward osmosis membrane, and can maintain the performance of a forward osmosis membrane can be provided.

It is a schematic diagram which shows the forward osmosis processing system in Embodiment 1. 6 is a schematic cross-sectional view showing a forward osmosis membrane module used in the forward osmosis treatment system of Embodiment 2. FIG.

  Hereinafter, an embodiment of a forward osmosis treatment system of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals represent the same or corresponding parts. In addition, dimensional relationships such as length, width, thickness, and depth are changed as appropriate for clarity and simplification of the drawings, and do not represent actual dimensional relationships.

(Embodiment 1)
The forward osmosis treatment system of this embodiment is a system capable of performing forward osmosis treatment in which water contained in FS is moved through a forward osmosis membrane into a draw solution having a higher osmotic pressure than the feed solution. .

  By forward osmosis treatment, for example, fresh water can be taken out from FS such as seawater, FS can be concentrated by taking out fresh water, and energy can be recovered from the osmotic flow. As a method for recovering energy, for example, a high concentration and high osmotic pressure DS (seawater or the like) is flowed to the first surface side of the forward osmosis membrane in a pressurized state, and a low concentration is flowed to the second surface side of the forward osmosis membrane. By flowing FS (fresh water, etc.) with low osmotic pressure at low pressure, fresh water moves to the DS side and the amount of pressurized seawater increases, and energy is obtained by rotating the turbine etc. with the increased pressure. A method is mentioned.

With reference to FIG. 1, the forward osmosis treatment system of the present embodiment basically has
(I) The forward osmosis membrane 10, the first chamber 21 to which the feed solution is supplied, and the second chamber 22 to which the draw solution is supplied. The first chamber 21 and the second chamber 22 are forward osmosis. Forward osmosis membrane module 1 partitioned by membrane 10;
(Ii) a water separation device 72 for separating water from the draw solution discharged from the second chamber 22;
(Iii) a discharge pipe 41 for discharging the draw solution from the second chamber 22 to the water separation device 72;
(Iv) a supply pipe 42 for supplying a draw solution concentrated by separating water in the water separator 72 to the second chamber 22;
(V) A bypass pipe 43 and a bypass pump 83 are provided for allowing a part of the draw solution in the second chamber 22 to flow into the supply pipe 42 for recirculation without passing through the water separator 72.

  In this embodiment, the feed solution contains a scale component. The scale component is a component dissolved in the feed solution, and is a component that generates scale (sediment) by precipitation. Examples of the scale component include calcium carbonate and magnesium carbonate. Examples of the feed solution containing the scale component include seawater, river water, brackish water, domestic wastewater, and oilfield or gasfield wastewater. In addition, the component which is not melt | dissolving may be contained in the feed solution.

  The draw solution is not particularly limited as long as it has a higher osmotic pressure than the feed solution. Examples of the draw solution include inorganic salt solutions, sugar solutions, and gases having high solubility in water (such as ammonia and carbon dioxide). And liquid containing organic matter, magnetic fine particles, or organic polymer. The draw solution may contain undissolved components.

  Although it does not specifically limit as a shape of a forward osmosis membrane, For example, a flat membrane, a spiral membrane, or a hollow fiber membrane is mentioned. In the present embodiment, a flat membrane as depicted in a simplified manner in FIG. 1 is drawn as the forward osmosis membrane. Although it does not specifically limit as a material of a forward osmosis membrane, For example, a cellulose acetate, polyamide, or polysulfone is mentioned. The forward osmosis membrane is assembled into a module for flowing FS and DS. The form of the module is not particularly limited, but when a hollow fiber membrane is used, an axial flow type module in which the hollow fiber membranes are arranged straight, a cross-wind type module in which the hollow fiber membrane is wound around a core tube, and the like can be mentioned. In the case of a flat membrane, a laminated module in which flat membranes are stacked, a spiral type module in which flat membranes are enveloped and wound around a core tube, and the like can be given.

  Hereinafter, the forward osmosis treatment system of the present embodiment will be described more specifically with respect to the case where FS is seawater and fresh water is produced from seawater.

The forward osmosis treatment system of this embodiment is
A pretreatment device 71 for pretreatment of the incorporated seawater;
A pretreatment drainage tank 78 connected to the pretreatment device 71 to which sludge and the like discharged from the pretreatment device 71 are sent;
A first chamber 21 of a forward osmosis membrane module 1 connected to a pretreatment device 71 via a pump 81 and supplied with pretreated seawater;
A concentrated seawater tank 79 connected to the first chamber 21 for collecting the seawater that has passed through the first chamber 21;
Forward osmosis membrane 10 of forward osmosis membrane module 1,
A second chamber 22 of the forward osmosis membrane module 1 to which DS is supplied;
A water separator 72 connected to the second chamber 22 via a discharge pipe 41 having a valve 91, to which the draw solution that has passed through the second chamber 22 is fed;
A DS adjustment device 73 connected to the water separation device 72 and connected to the forward osmosis membrane module 1 via a supply pipe 42 having a valve 92, a pump 82 and a control device 74;
A bypass pipe 43 connected to the second chamber 22 and connected between the control device 74 of the supply pipe 42 and the valve 92, and having a bypass pump 83;
A water storage tank 75 connected to the water separator 72 and to which water separated from the DS by the water separator 72 is sent;
Consists of

  The pretreatment device 71 is connected to the first end (upstream side) of the first chamber 21 of the forward osmosis membrane module 1, and the concentrated seawater tank 79 is connected to the second end of the first chamber 21 of the forward osmosis membrane module 1. It is connected to (downstream side). The DS adjustment device 73 is connected to the first end (upstream side) of the second chamber 22 of the forward osmosis membrane module 1 via the supply pipe 42, and the water separation device 72 is forward osmosis via the discharge pipe 41. The membrane module 1 is connected to the second end (downstream side) of the second chamber 22. The bypass pipe 43 is connected to the supply pipe 42 and the second end (downstream side) of the second chamber 22 of the forward osmosis membrane module 1.

  The pretreatment device 71 is a device for treating seawater taken by a pump (not shown) with sand filtration, UF membrane (Ultrafiltration membrane), MF membrane (Microfiltration membrane), cartridge filter, etc. Turbidity is removed, and water quality seawater suitable for the forward osmosis membrane module 1 can be obtained. If necessary, it is possible to add a pH adjusting means, a chlorine addition device, or the like.

  The forward osmosis membrane module 1 has a first chamber 21 and a second chamber 22 that are partitioned by the forward osmosis membrane 10. Seawater is supplied from the pretreatment device 71 to the first chamber 21, and the second chamber 22. DS is supplied from the DS adjustment device.

  A driving force corresponding to the difference in osmotic pressure between the feed solution and the draw solution is generated between the first chamber 21 and the second chamber 22 on both sides of the forward osmosis membrane 10. For this reason, if the osmotic pressure of the draw solution (high osmotic pressure solution) is made larger than the osmotic pressure of seawater, water can be recovered from the seawater into the draw solution.

The osmotic pressure of seawater and DS can be calculated from the following equation (1).
Π = iRTC (1)
In equation (1), Π is the osmotic pressure, R is the gas constant, T is the absolute temperature, C is the molar concentration of the solution, and i is the Phanto-Hoff coefficient. The Phanto-Hoff coefficient i is a coefficient representing the effect of ionization when the solute is an electrolyte. In the case of using a polymer for DS, it is known that the relationship between the concentration and the osmotic pressure does not apply to the Vanth-Hoff law. In that case, it is necessary to clarify the relationship between the concentration and the osmotic pressure in advance.

  The concentrated seawater discharged from the first chamber 21 of the forward osmosis membrane module 1 is sent to the concentrated seawater tank 79 and discharged to the ocean after the wastewater treatment operation.

  Next, the DS discharged after passing through the second chamber 22 of the forward osmosis membrane module 1 is sent to the water separator 72 via the discharge pipe 41 with the valve 91 opened. Here, the draw substance added to increase the osmotic pressure in the DS is separated from the water contained in the DS. As a separation method carried out by the water separation device 72, a method suitable for the type of the draw substance is selected. For example, in the case of inorganic salts, low melting point substances, etc., crystallization treatment, in the case of gas with high solubility in water, gas diffusion, in the case of magnetic fine particles, magnetic separation, in the case of sugar solution, ion exchange, stimulus-responsive polymer In this case, the stimulus (temperature, pH, electricity, magnetic field, light, etc.) can be selected. Examples of common separation methods include distillation and reverse osmosis membrane treatment.

  The separated water is sent to the water storage tank 75. The water stored in the water storage tank 75 is sent to the next purification step or the like as necessary.

  On the other hand, the DS containing a high concentration of the draw substance remaining after the water is separated is sent to the DS adjustment device 73. The osmotic pressure of DS sent to the DS adjusting device 73 varies depending on the specifications of the water separation device 72, but is at least higher than the osmotic pressure at the inlet of the water separation device 72.

  The DS whose temperature and the like have been adjusted by the DS adjusting device 73 is returned to the second chamber 22 of the forward osmosis membrane module 1 through the supply pipe 42 by the pump 82 with the valve 92 opened. Here, a part of the DS in the second chamber 22 is taken out from the first end (downstream side) of the second chamber 22 and is bypassed by the bypass pump 83 via the bypass pipe 43 with the valve 93 opened. The liquid is fed to the supply pipe 42 (without going through the water separation device 72). Thereby, DS supplied to the second chamber 22 can be diluted without using water.

  In the present embodiment, the control device 74 includes a measurement device for measuring the osmotic pressure of DS flowing in the supply pipe 42 immediately before flowing into the second chamber 22, and a control device for controlling the flow rate of the bypass pump 83. Including. The control device 74 controls the flow rate of the bypass pump 83 based on the DS osmotic pressure value measured by the measuring device. Accordingly, the water moves from the FS in the first chamber 21 to the DS in the second chamber 22, so that the concentration of the FS in the first chamber 21 when the feed solution is concentrated becomes the first chamber. 21, it can be controlled to be lower than the scale generation limit concentration (the sea level between the concentration generated by the precipitation of the scale component and the concentration not generated).

  Specifically, for example, the scale generation limit concentration is examined in advance for seawater supplied to the first chamber 21 of the forward osmosis membrane module 1, and the osmotic pressure difference between DS and FS and the concentration of the scale component in FS are determined. Thus, the osmotic pressure of DS when the concentration of the scale component in the FS reaches the scale generation limit concentration can be obtained as a reference value. The controller 74 controls the flow rate of the bypass pump 83 based on the DS osmotic pressure measurement value so that the DS osmotic pressure measurement value is smaller than the scale generation limit concentration.

  FS is gradually concentrated as it moves from the first end side (upstream side) to the second end side (downstream side) in the first chamber 21 of the forward osmosis membrane 10. Conversely, DS is gradually diluted as it moves from the first end side (upstream side) to the second end side (downstream side) in the second chamber 22 of the forward osmosis membrane 10. For this reason, in this embodiment, the osmotic pressure difference between DS and FS is particularly large in the first chamber 21 of the forward osmosis membrane 10 on the first end side (upstream side), and FS is locally concentrated to a high concentration. Therefore, it is easy to generate a scale. Therefore, it is preferable to control the amount of DS to be recirculated by the control device 74 or the like in consideration of the FS not reaching the scale generation limit concentration, particularly in such a portion where the scale is easily generated.

  In this embodiment, the case where the index value measured by the measurement device is osmotic pressure has been described, but other index values may be used depending on the type of the draw substance. For example, if the draw substance is a salt, the electrical conductivity may be measured, if the draw substance is a polymer, the viscosity, pressure loss or flow rate may be measured, and if the draw substance is a sugar, the refractive index is measured. May be.

  By the above treatment, forward osmosis treatment and water separation treatment are performed, and water can be continuously produced from seawater.

  In the forward osmosis treatment system of this embodiment, the DS supplied to the forward osmosis membrane module is diluted by mixing a part of the diluted and discharged DS with the DS supplied to the forward osmosis membrane module. The Thereby, it can prevent that the osmotic pressure difference of DS and FS becomes large too much, and can suppress the scale production | generation in the surface of a forward osmosis membrane. Therefore, a forward osmosis treatment system capable of maintaining the performance of the forward osmosis membrane can be provided.

  In this embodiment, the flow rate of the DS supplied to the forward osmosis membrane processing means is increased by recirculating a part of the diluted DS. As a result, the DS flow rate increases, the DS membrane resistance (concentration polarization resistance) decreases, and the effective concentration difference between DS and FS is maintained, so that the efficiency of forward osmosis treatment is improved.

  The reverse osmosis treatment is a process of collecting water by applying artificially strong pressure to move water from the high concentration liquid to be treated to the low concentration liquid (water etc.) side. Energy consumption for applying pressure is extremely high and energy efficiency is low. In contrast, forward osmosis treatment has the advantage of high energy efficiency.

(Embodiment 2)
This embodiment is different from Embodiment 1 in that a hollow fiber membrane module (see FIG. 2) having a hollow fiber membrane 10 as a forward osmosis membrane is used as the forward osmosis membrane module 1. In addition, the overlapping description about the same point as Embodiment 1 is abbreviate | omitted here.

  Referring to FIG. 2, the hollow fiber membrane module of the present embodiment includes a porous pipe 3 having a plurality of holes 3 a arranged at the center, a plurality of hollow fiber membranes 10 arranged around the porous pipe 3, A hollow fiber membrane element including a pipe 3 and a resin wall 61 that fixes the plurality of hollow fiber membranes 10 at both ends thereof is provided. The plurality of hollow fiber membranes 10 have openings at both ends. The hollow fiber membrane element is held in a state where an O-ring 51 a is interposed in the holding member 51.

  In the hollow fiber membrane module of the present embodiment, the low osmotic pressure FS flows through the inside 21 (first chamber) of the hollow fiber membrane 10, and the high osmotic pressure DS is outside the hollow fiber membrane 10 (second chamber). Flowing. That is, FS supplied from the FS supply port 11 a flows into the inside 21 (first chamber) of the hollow fiber membrane 10 from the first opening 10 a of the hollow fiber membrane 10, and the second opening of the hollow fiber membrane 10. 10b flows out of the module through the FS discharge port 11b. Further, DS supplied from the DS supply port 12a flows into the porous pipe 3 and is supplied to the outer side 22 (second chamber) of the hollow fiber membrane 10 through the plurality of holes 3a, and from the DS discharge port 12b. It is taken out.

  In Embodiment 1, such a hollow fiber membrane module can be used instead of the forward osmosis membrane module 1 having a flat membrane-like forward osmosis membrane.

  FS is gradually concentrated as the interior 21 (first chamber) of the hollow fiber membrane 10 moves from the first opening 10a side to the second opening 10b side. On the other hand, since DS is supplied from the DS supply port 12 a and flows into the porous pipe 3, fresh and high osmotic pressure DS is always supplied to the outside of the hollow fiber membrane in the vicinity of the porous pipe 3. Thereby, since FS which flows through the inside 21 (first chamber) of the hollow fiber membrane in the vicinity of the porous pipe 3 is concentrated to a high concentration, scale is likely to be generated in the vicinity of the porous pipe 3.

  In addition, when flowing FS to the outside 22 of the hollow fiber membrane and flowing DS to the inside 21 of the hollow fiber membrane, the FS moves the outside 22 of the hollow fiber membrane 10 from the porous pipe 3 side to the pressure vessel 15 side. As it gradually concentrates. In this case, since DS flows from the DS supply port 11a and flows from the first opening 10a to the inside 21 of the hollow fiber membrane, the first opening 10a side is always fresher than the second opening 10b side. DS with high osmotic pressure is supplied. Thereby, since the FS flowing through the first opening 10a side is concentrated to a high concentration, scale tends to be generated on the first opening 10a side.

  Therefore, it is preferable to control the amount of DS to be recirculated by the control device 74 or the like in consideration of the FS not reaching the scale generation limit concentration, particularly in such a portion where the scale is easily generated.

  DESCRIPTION OF SYMBOLS 1 Forward osmosis membrane module, 10 Forward osmosis membrane (hollow fiber membrane), 10a 1st opening part, 10b 2nd opening part, 11a FS supply port, 11b FS discharge port, 12a DS supply port, 12b DS discharge port, 13, 14 Wall member, 15 Pressure vessel, 21 1st chamber (inside of hollow fiber membrane), 22 2nd chamber (outside of hollow fiber membrane), 3 porous pipe, 3a hole, 41 discharge pipe, 42 supply pipe, 43 bypass Pipe, 51, 52 Holding member, 51a, 52a O-ring, 61, 62 Resin wall, 71 Pretreatment device, 72 Water separation device, 73 DS adjustment device, 74 Control device, 75 Water storage tank, 78 Pretreatment drainage Tank, 79 Concentrated seawater tank, 81, 82 pump, 83 Bypass pump, 91, 92, 93 Valve.

Claims (2)

A forward osmosis treatment system capable of transferring water contained in a feed solution through a forward osmosis membrane into a draw solution having a higher osmotic pressure than the feed solution,
The forward osmosis membrane, a first chamber to which the feed solution is supplied, and a second chamber to which the draw solution is supplied, wherein the first chamber and the second chamber are the forward osmosis membrane. A forward osmosis membrane module,
A water separator for separating water from the draw solution discharged from the second chamber;
A discharge pipe for discharging the draw solution from the second chamber to the water separator;
A supply pipe for supplying the draw solution concentrated by separating water in the water separator to the second chamber;
A bypass pipe and a bypass pump for allowing a part of the draw solution in the second chamber to flow into the supply pipe and recirculate without passing through the water separator ;
The feed solution includes a scale component;
The concentration of the feed solution in the first chamber when the feed solution is concentrated when water moves from the feed solution in the first chamber to the draw solution in the second chamber is the first solution. A forward osmosis treatment system further comprising a control device for controlling a flow rate of the bypass pump so that a scale is lower than a scale generation limit concentration generated by precipitation of the scale component in one room . The control device includes a measuring device for measuring the osmotic pressure of the draw solution flowing in the supply pipe immediately before flowing into the second chamber, and based on the value of the osmotic pressure measured by the measuring device. The forward osmosis treatment system according to claim 1 , wherein the forward osmosis treatment system is a device that controls a flow rate of the bypass pump.

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